1. Field of the Invention
This invention relates to thermodilution catheter assemblies for determining cardiac output and, more particularly, to the assembly for electrically connecting the catheter to an output computer.
2. Description of Prior Art
The use of thermodilution catheters to determine cardiac output is well-known. The catheters are typically small-diameter balloon catheters equipped with distal temperature sensing means and a lumen opening a short distance proximal to the temperature sensing means for introducing a low temperature liquid injectate into the blood stream. The displacement of temperature resulting from the introduction of the injectate into the blood stream is sensed by the temperature sensing means, and the magnitude and duration of temperature displacement is used to compute the blood flow rate or cardiac output. A representative thermodilution catheter is illustrated in U.S. Pat. No. 3,995,623.
The blood flow rate is computed from the displacement of blood temperature according to the Stewart-Hamilton dilution equation for a thermal indicator as described in U.S. Pat. No. 3,987,788. In accordance with the teachings of this reference, numerical values are manually entered into the system for a computation constant, blood temperature, and injectate temperature. The computation constant is derived from the composition of the injectate, the volume of injectate, and a correction factor for the rise in temperature of the injectate as it passes through the lumen of the catheter to the injectate orifice. The computation constant for any given set of operating conditions is selected from a table provided by the computer manufacturer and is manually entered into the system by the operator.
In the vast majority of cases, the thermodilution technique is carried out with a standard five percent (5%) glucose solution, and a standard injectate volume for a given size catheter. Thus, a single computation constant is used in most cases for any given sized catheter. It is accordingly an object of the present invention to provide a means for automatically entering a standard computation constant for a given size catheter into the computer when the catheter is connected, the computer being provided with manual override means in the event nonstandard thermodilution conditions are employed.